Cutting inserts are metal cutting tools for machining of metal by milling, drilling or turning or by similar chip forming methods. Cutting inserts are produced by powder metallurgical methods from a metallic powder, for example a mixture comprising tungsten carbide and cobalt, such as a cemented carbide powder, or from a ceramic powder, for example a mixture comprising aluminum oxide, silicon nitride and silicon carbide. Cutting inserts may also be manufactured from cermets, for example from a mixture comprising titanium carbide and nickel, or other materials such as, for example, cBN materials. The powder is compacted into a cutting insert green body by opposing first and second punches in a die cavity. After compaction, the cutting insert green body is removed from the die cavity and subjected to sintering into a strong cutting insert.
Typically, cutting inserts are provided with a through-hole by which the cutting insert may be attached to a tool holder by means of a screw or pin.
In manufacturing of certain types of cutting inserts, so called “tangential inserts” or “cross-hole inserts” the through-hole is formed by a core rod which is inserted into the die cavity in a direction which is non-parallel to the main pressing direction.
A problem related to the manufacturing of tangential inserts is that the non-parallel arrangement of the core rod in relation to the main pressing direction causes the density distribution in the cutting insert green body to vary around the through-hole. When the cutting insert green body shrinks during sintering, the uneven density distribution causes the through-hole to deform.
Various attempts have been made in the past to solve this problem.
WO2009/085002 describes a method which uses a core rod that is divided into a separate male and female part to form the through-hole. During the compaction step, the male and female core rod parts are pressed into each other to increase the density of the powder around the through-hole. Although proven successful to some extent, the method of WO2009/085002 leaves room for further improvement of the dimensional accuracy of the through-hole. The method of WO2009/085002 further involves the use of complicated designed core rods and multi axial pressing equipment.
In U.S. Pat. No. 6,986,866 B2 a core rod of non-circular cross-section is used to form the through-hole in order to compensate for deformation of the through-hole during sintering. However, due to difficulties in predicting and matching deformation of the through-hole with the shape of the core rod, the method of U.S. Pat. No. 6,986,88 B2 does not provide through-holes of high dimensional accuracy in the sintered cutting insert.
Consequently, it is an object of the present disclosure to provide a method which allows for manufacturing of cutting inserts with a through-hole with improved dimensional accuracy. A further object is to provide a simple and cost effective method of manufacturing cutting inserts with a through-hole with improved dimensional accuracy. It is also an object to provide an arrangement which allows for manufacturing of cutting inserts having through-holes with high dimensional accuracy.